The present invention relates generally to a gasification system and process for converting generally solid feedstock such as carbonaceous material into desirable gaseous products such as synthesis gas. The gasification system and process must be designed to be simple, yet maximize carbon conversion efficiency.
Three basic types of system and processes have been developed for the gasification of carbonaceous materials. They are: (1) fixed-bed gasification, (2) fluidized-bed gasification, and (3) suspension or entrainment gasification. The present invention relates to the third type of system and process-suspension or entrainment gasification. More particularly, the present invention relates to a two stage entrained gasification system and process for gasifying carbonaceous materials.
The flexibility of the two stage gasifier design can be exploited by maximizing the slurry feed rate to the lower temperature second stage, thereby utilizing the heat generated in the first stage gasifier to evaporate water from the slurry. The char and unconverted carbon exiting the second stage gasifier are then separated and recycled back to the first stage gasifier in dry form, thus minimizing the amount of oxygen required in the higher temperature first stage and maximizing the conversion efficiency of the gasifier.
One problem with feeding to the lower temperature second stage is that the tar produced during the pyrolysis of the coal or petroleum coke is not adequately destroyed. The undestroyed tar condenses when the syngas is cooled, thereby fouling the heat exchange surfaces or plugging up the filters downstream. Technology is needed that allows increased feedstock addition to the lower temperature second stage of the gasification reactor, while minimizing the production of tar.